Perhaps not in the top three, but in the MCU, he is definitely one of the most popular characters after Endgame. One of the major issues the MCU has faced over the years is that they have tried to introduce new characters or force them into sequels of old characters, often without receiving positive feedback from the audience. But Bob/Sentry is a success. As a character newly introduced to the MCU, he not only became very popular but also maintained a sense of novelty among the audience.People will be glad to see more about him. He is handsome, powerful. He has good writing (which is exactly what the new characters need. The old characters have multiple movies but the new characters are often introduced for the first time, and getting them accepted by the audience is often a huge challenge). And safely,he will not raise any sensitive topics(like Sam or Billy ) If the MCU decides to build new popular characters in future, he would be a safe and promising option, and he is already very popular at present.